Various methods and apparatuses are disclosed in the prior art for forming metal tubes. For example, U.S. Pat. No. 2,450,580 entitled "TUBE BENDER" issued on Oct. 5, 1948 to John E. Conzelman, Jr. This patent discloses a tube bender which uses hydraulic pressure in combination with a ram to force a tube blank, having the majority of its length outside the die through the curved die. This patent teaches the use of hydraulic pressure alone in order to form curved tubes in certain instances. Where necessary, an additional force is applied by a mechanically acting ram. Pressure control inside the closed tube is allowed by an exhaust means. Additionally, interior pressure may be supplemented by the use of non-compressible balls, each having a diameter slightly less than that of the interior diameter of the tube blank.
U.S. Pat. No. 2,183,702 entitled "DIE ASSEMBLY FOR FORMING HOLLOW METAL ARTICLES" on Dec. 19, 1939 issued to Frans W. Wendel. It teaches the use of tube blanks filled with oil and forced into a curved die by means of plungers until the blanks at least initially form arcuate shapes. Wendel indicates that it may quite often be necessary to form a shape in two or three steps using this method to produce a tube with a blunt end.
U.S. Pat. No. 3,625,040 entitled "METHOD AND APPARATUS FOR FORMING ARTICLES FROM A TUBULAR BLANK", issued on Dec. 7, 1971 to William J. DeGain. This patent teaches the use of hydrostatic metal forming wherein the pressure developed from inside the tube blank causes a tube to deform within the contours of a die assembly. The whole die assembly is submerged preferably in water, although other hydraulic fluids are cited, and hydraulic pressure is applied to the interior of the tube blank sufficient to cause deformation. Both ends of an open tube are plugged, although passageways to the hydraulic pressure source are found within the plug. The tube blank does not force its way through the die, rather it is caused to adopt the contour shape of the die that is being impressed against it.
U.S. Pat. No. 203,842 entitled "METHOD OF BENDING PLUMBERS' TRAPS" issued on May 21, 1878 to Edwin A. Leland It discloses the use of a fluid filled lead pipe that may be bent into arcuate shapes without collapsing at tight radii. The use of hydraulic pressure is disclosed in Leland for the purpose of assisting in the deformation of the lead piping. According to the patent, pressurizing a tube with fluid while in a die is known, such that Leland is distinct in not requiring a die. The primary reliance in this patent is placed on the flexibility and ductility of the subject metal.
U.S. Pat. No. 3,328,996 entitled "DEVICE AND METHOD FOR MANUFACTURING ELBOW FITTINGS FROM STRAIGHT TUBING", issued on Jul. 4, 1967 to P. H. Pin, et al. The patent discloses the use of a pressure ram that supplies a constant force on a substantially incompressible medium placed inside the tube blank. The tube blank is then inserted into a die where the top half is subject to displacement laterally, and is coordinated with a cavity in the die which allows formation of the tube into a curved form with nominal loss of internal dimensional integrity. This patent describes the use of various medium that has been used in the prior art, such as sand, water, oil, rubber, etc.
U.S. Pat. No. 2,918,201 issued on Dec. 22, 1959 to A. A. Klein and is entitled "APPARATUS FOR BENDING TUBE BLANKS". This patent teaches the use of a ram with associated die with allowances for a controlled pressure condition. The ram is assisted by the use of an incompressible medium that tends to exhibit fluid characteristics. This medium may be of rubber or synthetic plastics. The pressure control occurs through the exit port of the die. The patent also discloses the use of a ram to cause the tube blank to proceed through the die.
U.S. Pat. No. 2,837,810 issued on Jun. 10, 1958 to Carl R. Ekholm and is entitled "METHOD OF PRODUCING FITTINGS". This patent discloses the use of a tube blank where both ends are sealed, but where one end is allowed to receive a port for hydraulic application. A blank thus inserted into a die form can be pressurized to the extent necessary to adopt the form of the die. Deformation of the tube blank along those portions of the die where clearance exists is allowed to take place under high hydraulic pressure. The tube blank is not forced through the die but rather reacts to the pressure applied internally.
U.S. Pat. No. 3,243,873 issued on Apr. 5, 1966 to Homer J. Steel and is entitled "TUBE BENDING". This patent utilizes an axial roller device that engages suitably shaped "free mandrels" that are placed into the interior of the tube blank. As the blank is forced through the access portion, the free mandrels are compatibly guided by the axial roller, causing an incremental bending action near the end of the tube.
Therefore, it is an object of the present invention to provide an improved method and apparatus for making an irregularly shaped drawn tube or element.
Another object of the present invention is to provide a method and apparatus which are efficient to operate and are capable of producing an irregularly shaped drawn tubular element in a short period of time, as an example, 5 to 10 seconds.
Still another object of the present invention is to form a tube closed at one end into almost any shape by forcing the tube through a form mold by use of hydraulic and mechanical pressures and by controlling the speed of the formation of the displaced metal by the use of hydraulic pressure from the opposite end of the tube.
It is further an object of the present invention to discloses a method of initially setting up an apparatus for making irregularly shaped drawn tube, wherein the operating pressures are controlled to ensure that the irregularly shaped tube will not have bends at any curved portions in the shaped tube.